The BGS Lexicon of Named Rock Units — Result Details

Hunstanton Formation

Rubbly to massive chalks with marl bands; typically pink to brick-red (due to disseminated haematite), but locally the upper part is grey due to secondary alteration of the iron minerals. The lower part of the formation is commonly weakly sandy. No formal subdivisions. The Hunstanton Formation as defined by Mitchell (1995), describing the thick succession at Speeton in the Cleveland Basin, is divided into five members. These are in ascending order the Queens Rocks Member, Speeton Beck Member, Dulcey Dock Member, Weather Castle Member and the Red Cliff Hole Member.

Definition of Lower Boundary:

The base is a sharp or (apparently) gradational boundary with marly chalk of the formation overlying ferruginous sandstones of the Carstone Formation or (in the Cleveland Basin) mudstone of the Speeton Clay Formation; commonly marked by a line of phosphatic nodules as burrow-fills.

Definition of Upper Boundary:

The top is an erosion surface, locally developed as a hardground, with hard red limestone overlain by nodular chalk (lowest Cenomanian) of the Paradoxica (or Sponge) Bed or (in the Cleveland Basin) Crowe's Shoot Member (Mitchell, 1995); this horizon (the base of the Lower Chalk in Norfolk, or elsewhere of the Ferriby Formation) may or may not correspond with the upper limit of red chalks.

Thickness:

About 1m at the type section in Norfolk, typically 3m in Lincolnshire and south Yorkshire, thinning over the Market Weighton High, but expanding to an estimated 30m in the Cleveland Basin with about 24m exposed in the cliffs at Speeton.

Geographical Limits:

Present throughout Yorkshire (including the Cleveland Basin where it attains its maximum development) and Lincolnshire and extends southwards to its type locality of Hunstanton on the north Norfolk coast. The formation passes laterally into the Gault Formation south of Dersingham in Norfolk.

Jeans, C V. 1980. Early submarine lithification in the Red Chalk and Lower Chalk of Eastern England; a bacterial control model and its implications. Proceedings of the Yorkshire Geological Society, Vol.43, 81-157.